We’re publishing this as an emergency bulletin for our customers and the larger web community. A few hours ago a zero day vulnerability emerged in the Tor browser bundle and the Firefox web browser. Currently it exploits Windows systems with a high success rate and affects Firefox versions 41 to 50 and the current version of the Tor Browser Bundle which contains Firefox 45 ESR.

If you use Firefox, we recommend you temporarily switch browsers to Chrome, Safari or a non-firefox based browser that is secure until the Firefox dev team can release an update. The vulnerability allows an attacker to execute code on your Windows workstation. The exploit is in the wild, meaning it’s now public and every hacker on the planet has access to it. There is no fix at the time of this writing.

Currently this exploit causes a workstation report back to an IP address based at OVH in France. But this code can likely be repurposed to infect workstations with malware or ransomware. The exploit code is now public knowledge so we expect new variants of this attack to emerge rapidly.

This is a watering hole attack, meaning that a victim has to visit a website that contains this exploit code to be attacked. So our forensic team is keeping an eye on compromised WordPress websites and we expect to see this code show up on a few of them during the next few days. An attackers goal would be to compromise workstations of visitors to WordPress websites that have been hacked.

Since then researcher Dan Guido posted a series of tweets with some analysis of the exploit itself.

Twitter user @TheWack0lian noticed the shellcode (code that executes on your Windows workstation once exploited) is very similar to shellcode likely used by the FBI back in 2013 to deanonymize visitors to child porn websites hosted by FreedomHosting. The FBI confirmed that they compromised that server and days later it was serving malware that would infect site visitor workstations. The code then reported site visitor real IP addresses, MAC addresses (network card hardware address) and windows computer name to a central server. This code is very similar.

What we found

The shell code in this attack calls back to IP address 5.39.27.226, which was a web server hosted at OVH in France. The site is now down. Our own research shows that if you look up this IP address in Shodan, it had an SSL certificate that is a wildcard for the energycdn.com domain name. That site for energycdn is simplistic and according to archive.org, it has not changed since 2014.

One could speculate that the server at 5.39.27.226 was used by energycdn.com as one of their servers to host pirated content. Perhaps the server was compromised by whoever controls energycdn to host that content and then was reinfected by the perpetrator of this new malware variant. But we’re speculating.